This invention is related to a machine tool, and particularly, to a microfinishing machine for workpieces such as internal combustion camshafts operating on a centerless turning principle.
Numerous components for machines require microfinishing operations which produce high quality surface finishes of known characteristics. Microfinishing of surfaces is necessary to ensure proper friction and wear properties of the components in use. Microfinishing is especially significant where sliding contact between surfaces occurs during operation of a machine. Internal combustion engines of modem day motor vehicles include numerous components having microfinishing requirements. Crankshafts, which convert the reciprocating motion of the pistons into a rotary output, have numerous cylindrical journal surfaces which require microfinishing. The assignee of this invention, the Industrial Metal Products Corporation (IMPCO), has been an innovator of numerous machines and processes in the microfinishing area, particularly oriented toward crankshaft microfinishing. U.S. patents on these innovations include U.S. Pat. Nos. 4,682,444; 5,095,663; 5,148,636; and 5,531,631; which are hereby incorporated by reference.
In addition to internal combustion engine crankshafts, camshafts also require microfinishing. Camshafts typically have a number of cylindrical surfaces formed on them, rotating within simple journal bearings in the engine. Typically, a belt, chain, or gear, drives the camshaft to rotate in a synchronized manner with the rotation of the crankshaft. A number of cam lobes along the camshaft interact with cam followers to actuate the valves which control the intake and exhaust processes within the engine. In a typical four-stroke, internal combustion engine, two lobes are devoted to each cylinder, with one lobe controlling the intake valve and the other controlling the exhaust valve. More sophisticated internal combustion engines use multiple intake and exhaust valves per cylinder and require a corresponding increase in the number of lobes formed on the camshaft (or camshafts). Both the journal bearing surfaces and the cam lobe surfaces of the camshaft often require microfinishing operations. Camshaft blanks are normally formed from cast iron. The rough castings are machined in a number of steps including grinding operations to form the journal and cam surfaces. Microfinishing of camshafts is a known process which has been in use for many decades. In one process in use, the camshaft is turned between fixed centers in the manner of a lathe, with microfinishing tools acting on the bearing journal surfaces, and at a separate station, on the lobe surfaces. So-called xe2x80x9ccenterlessxe2x80x9d approaches are also known. In a centerless machine, a pair of rollers frictionally engage the cylindrical journal surfaces (or another cylindrical surface of the workpiece) and cause the camshaft to rotate. An abrasive tool, such as a stone or an abrasive-coated film may be used. An example of the centerless machine for the machining of ground shafts is found with reference to U.S. Pat. No. 5,231,798, which is hereby incorporated by reference and which is assigned to the assignee of this application.
In any machining process for workpieces, it is desirable to reduce the number of individual stations where metal finishing operations are completed. By reducing the number of stations, the part handling equipment is made simpler. Moreover, the probability for damage to workpieces, caused by mishandling, is reduced where individual stations can be eliminated. Plant floor space is also reduced in such conditions. The structure for the machine tools and drive system adds cost where multiple stations are required. In present microfinishing operations of camshafts, the machining of the cam lobes and journals occurs at different stations. This results in dedicated individual machining centers required for those surfaces.
In view of the foregoing, it is the object of this invention to provide a microfinishing machine which enables journal and camshaft lobe surfaces of a camshaft to be machined in a single operation by one machine. Workpiece handling is also facilitated through the use of a centerless system for the microfinishing machine.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.